This invention relates to fluid filters and methods of constructing fluid filters and more particularly to fluid filters used in air-makeup filtration systems.
Fluid filters, particularly air-makeup filters for commercial and residential buildings, have been known for some time. For example U.S. Pat. No. 2,138,736, issued to Gaarder, provides a filter pad comprised of a fibrous material between a top screen and a bottom screen of very coarse grid. The fibrous material extends beyond the edges of the screens. The top and bottom screens are joined and, at the same time, rigidly separated by posts, which are welded to the lower screen and provided with open hooks, which in assembling the pad are passed over the upper grid and closed. The fibrous material extends beyond the edges of the screens to provide a dust seal when the assembled filter is placed into a frame.
Another example is U.S. Pat. No. 2,685,345, issued to Lindner, which provides an air filter pad having holder frames comprised of continuous border frames and crossed members. The crossed members are diagonally disposed and are welded at their ends to the corners of the border members. The holder frames are held upon a filter pad by means of inwardly facing u-shaped clips. The arms of these clips overlap the frame border members and terminate in outwardly facing hooks. The arms of the clips are engaged with the border members of the frame by compressing a filter pad through pressure applied to the opposed portions of the border frames until the arms of the clips and their outwardly facing hooks can be slipped over the border members. The edges of the filter pad material will extend beyond the holder frames and are compressible edges so that the filter may be inserted and self supported in conduits or ducts of considerable variation in dimensions.
There are several drawbacks to the air filters known in the art. The known air filters require a rigid frame on each side of the filter pad and the opposing frames must be cross-connected to retain the filter pads within the frames. This construction requires considerable assembly and relatively expensive materials. Because of the expense of the rigid frames and filters the prior filters are designed to allow cleaning and/or replacement of the filter pads. The rigid frames are bulky and require relatively greater shipping and storage space. The presence of metal screens and cross members to support the central portions of the filter pad present a danger to downstream equipment. As the filters become laden with filtered matter the pressure drop across the filter increases. This pressure drop is supported by the cross members and screens in the central portion of the filter. Eventually the screens or cross members may fatigue and rupture sending portions of the screen and cross members into the downstream equipment.